1. Field of the Invention
A magnetorheological fluid-based hydraulic mount apparatus for supporting a vibration source on a base.
2. Description of the Prior Art
Conventional hydraulic mounts exist for supporting and providing vibration isolation of vibration sources. One well-known application of these mounts is for supporting components of automotive vehicles. These mounts typically operate to provide engine vibration isolation while also controlling the motion of the engine and connected powertrain components with respect to the vehicle frame or body structure. In many applications of engine and powertrain mounts, it is desirable to vary damping characteristics of the mount to provide selective isolation of vibrations at certain frequencies.
Magnetorheological fluid-based vibration damping mounts have been developed to isolate or dampen vibrations at multiple frequencies. Magnetorheological fluid, as known in the art, is responsive to a magnetic field to modify its shear properties. Specifically, it has the ability to reversibly change from a free-flowing, linear, viscous liquid to a semi-solid with controllable yield strength when exposed to a magnetic field. These magnetorheological fluid-based mounts use this characteristic of the fluid to control the spring and damper rates when required.
One such magnetorheological fluid based mount is disclosed in U.S. Pat. No. 6,622,995 to Baudendistel et al. The mount includes a housing that extends about and along a first axis and defines a housing chamber. A flexible body made of an elastic material is partially disposed in the housing chamber and is interconnected with the housing for deforming elastically in response to movement of the vibration source relative to the housing caused by an external excitation. The flexible body extends radially about and along the first axis. A diaphragm made of an elastic material is disposed in the housing chamber and is spaced axially from the flexible body.
A partition assembly is disposed in the housing chamber between the flexible body and the diaphragm for dividing the housing chamber into a pumping chamber between the flexible body and the partition assembly, and a receiving chamber between the partition assembly and the diaphragm. The volume of each of the chambers is changed by deformation of the flexible body and the diaphragm in response to the external excitation. A sensor is disposed on an automotive vehicle for measuring a vibration condition of the vehicle in response to the external excitation and producing a corresponding vibration frequency signal. A magnetorheological fluid is contained within the pumping and receiving chambers. The partition assembly defines a main fluid passage that extends axially between the pumping and receiving chambers to establish fluid communication between the pumping and receiving chambers for passing the fluid therebetween in response to deformation of the flexible body and the diaphragm.
The partition assembly includes a plurality of electromagnet coils disposed adjacent to the main fluid passage for variably generating a magnetic flux across the main fluid passage for modifying the shear resistance of the fluid passing through the main fluid passage to variably change the dynamic stiffness of the mount apparatus.
Due to the mass of the magnetorheological fluid in magnetorheological fluid-based damping mounts, it is known for the dynamic spring rate to be undesirably high at certain frequencies, like the idle frequency of automotive vehicles. It is desirable to reduce the dynamic spring rate at these frequencies to reduce the vibrations felt by operators.
It is also known in the art for non-magnetorheological fluid based hydraulic damping mount apparatuses to include a rate dip track passage defined by a partition assembly and extending between pumping and receiving chambers for oscillating fluid therethrough to create a “rate dip” effect, or decrease in the dynamic stiffness of the mount apparatus at predetermined vibration frequencies. One such mount is disclosed in U.S. Pat. No. 6,592,110 to Takashima et al. on Jul. 15, 2003. However, a known issue with such mounts is that a “rate rise” or sharp increase in dynamic stiffness of the mount occurs at vibration frequencies above the predetermined rate dip frequency because fluid flows through both the rate dip track passage and a primary fluid passage, causing an overlap of the frequencies that the two passages are effective at.